A still — Volcano — Life —

A still — Volcano — Life —
That flickered in the night —
When it was dark enough to do
Without erasing sight —

A quiet — Earthquake Style —
Too subtle to suspect
By natures this side Naples —
The North cannot detect

The Solemn — Torrid — Symbol —
The lips that never lie —
Whose hissing Corals part — and shut —
And Cities — ooze away —
                                       F517 (1863)  J601

The volcano symbolizes a certain way of being alive. Could it be a poet's way (whose lips "never lie"), a woman's whose life amid a patriarchal Calvinist family and society meant her strongest passions and questings must either be silent or rupturing? I think so, and this is not the only Dickinson volcano poem that attentive readers and scholars suggest are a self portrait. 
The poem is full of paradoxical phrasings: the Volcano Life is "still"; the Earthquake is "quiet; and the Symbol (the volcano standing for the poet/speaker) is both "Solemn" and "Torrid".  The first two stanzas hint at the volatility and upheaval beneath the poet's surface. The Volcano is only flickering, and this at night. Related earthquake activity is so "subtle" that those north of or on the other side of the ocean from Vesuvius (the famous volcano near Naples, Italy) cannot detect it. These would be the cooler, more restrained types – think New Englanders or northern Europeans – unlike those hot-blooded Mediterraneans.  

Yet the third stanza warns that despite the lulling quiet, the volcano/poet need only part her coral lips, just open and shut them, and the resulting eruption will destroy any cities in its path. Yikes! 

There's a nightmare quality to the poem. We see the poet in her room, her passions roiling beneath the surface. She is writing at night where her poetic sight is clearest and where others won't get a glimpse of the hot light she keeps damped within. We see the tremors of her soul, moved by large questions, powerful emotions, and startling visions. In a bit of a dig, she suggests that while some people would sense her power and heat,  most are unacquainted with volcanoes; their emotional or spiritual climate is too cool. I am reminded of "More Life – went out – when He went" (F415) where she contrasts the "Peat life" to that of the flame-proved anthracite. The peat people ignore the existence of volcanoes.
In the monstrous last stanza Dickinson gives us a glimpse of her power. There is nothing coy, nothing humble, and nothing ladylike about it – although it is completely female. Her façade is "Solemn" for she is fully aware of herself. Her deeper nature is scorching, burning with heat. Her lips never lie, and when they open the erupting magma hisses and flows, whole cities destroyed as they "ooze away" in its flow. Now that's poetry!
That last image gains double power from the doubled image of the poet's lips. They are the guardian gates to the eruptive truths Dickinson hammers in the forge of her soul. "Dare you see a Soul at the 'White Heat'?" she asks in another poem (F401). They are at the same time labial which if opened would release a hot flood of female sexuality. Their flow is like magma, its force lethal for those in its path. The idea of "ooze" is primordial.

As a final note, Dickinson differentiates the North from the South in "Our lives are Swiss" (F129) where the northerners are "still" and "Cool" while on the other side of the Alps, the Italians live in earthy and hot passion.